Electrical inverters



plane Company, Seattle, Wash., a corporation of Dela- Ware nnen Jury 27,1959, ser. No. s29,s22 s claims. (ci. 'ssi-112) This invention relatesto ia regulated flybaclf; inverter and, more particularly, to one thatis suitable for use `as an electronic photo-flash circuit.

ln an electronic photo-flash circuit, a load capacitor is charged upfrom a low initial voltage to some higher voltage. A photo-flash bulb isconnected across the load capacitor `and when -a flash exposure isdesired, the cir- `cuit is completed so that the load capacitor isdischarged through the photo-flash bulb. Various types of invertercircuits, such as the Royer inverter, have heretofore been utilized asan electronic photo-dash circuit. However, such prior art circuits, suchas the Royer inverter, have several limitations when utilized las aphoto-hash circuit. For instance, the energy transfer efficiency incharging up the load capacitor from zero initial voltage to some highervoltage has a theoretical fifty percent upper limit. The reason for thisis that these prior art inverters such as Royers have an equivalentoutput circuit comprising a constant voltage in series with a resistor.Thus, the recycle time for the photo-hash circuit is increased due tothis inefficient transfer of energy while charging up the loadcapacitor. In addition, owing to the circuitry of these prior iartinverters, a relatively high back voltage `appears across the output orpower rectifier. Therefore, the power rectifier when so utilized musthave a high voltage rating, thus increasing its cost.

ln accordance with this invention, a flyback power inverter, having atwo step energy transfer process and unique regulating means, isutilized as the electronic photo-i ash circuit. Presently usedelectronic photo-hash circuits do not utilize the flyback principle. Ofcourse, ilyback circuits of themselves are well known in the art `andmeans have heretofore been provided for regulating the output voltage ofa flyback circuit. However, the prior lart regulating means for aiiybacl; inverter when utilized as an electronic photo-flash circuit hasseveral disadvantages. One disadvantage is that the regulation isasymptotic and thus a transient condition exists before a substantiallyconstant regulated value is reached. This would increase the recycletime for an electronic photoash circuit if such a prior art regulatedflyback inverter were utilized. Further, most `known types of regulatorsfor flyback inverters control the current level to the 1nput or powerwinding of the inverter at the instant the flybaclt occurs. Thus, thefrequency of operation of the associated power transistor is increasedwhen the ilyback inverter is regulating at the terminal voltage. Thlsrelatively high frequency of operation of the power transistor effects ahigher energy loss in the overall system due to the higher number oftransistions that the power transistor makes in going from the on to theoft condition. Further, the 4average core losses in these prior yartinverters when regulating `at the terminal voltage are greater.Therefore, the over-all eliiciency of these prior art regulated iiybacl:inverters is relatively low.

An object of this invention is to provide for charging a capacitive loadfrom a low initial voltage to some higher voltage at a higher energytransfer efiiciency.

Another object of this invention is to provide for reducing the recycletime in electronic photo-flash circuits by utilizing a fiyback powerinverter having a high energy transfer efficiency in charging acapacitive load from a low initial voltage to some higher voltage.

nited States Patent A further object of this invention is to provide anew `and unique means Ifor regulating the output tenninal voltage of aiiyback power inverter so that the terminal voltage is substantiallyindependent of the magnitude of the output voltage of the direct-currentinput source.

Still another object of this invention is to provide voltage regulationfor a flyback power inverter which is nonasymptotic so as to furtherreduce the recycle time when the inverter is utilized for instance as anelectronic photoflash circuit.

A still further object of this invention is to provide for so regulatinga flyback power inverter that the power transistor operates Iat arelatively low frequency when regulating at the terminal voltage, thusminimizing the total energy loss in the system over a period of time bythe action of the transistor in going from the on to off condition.

Another object of this invention is to provide an inverter suitable foruse `as `an electronic photo-flash circuit in which the output or powerrectifier can have a lower voltage rating.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with the accompanying drawing inwhich:

FIG. l is `a schematic diagram of the apparatus and circuitsillustrating one embodiment of this invention;

FlG. 2 is a schematic diagram of the `apparatus and circuitsillustrating another embodiment of the teachings of this invention inwhich improved starting means is provided for the yback inverter.

Referring to FlG. l there is illustrated a regulated ilyback powerinve-rter 1i) illustrating one embodiment of the teachings of thisinvention. In operation, the regulated iiyback power inverter 10 chargesIa load or output capacitor 12 from a low initial voltage to some highervoltage Iat a high energy transfer eiiciency between an inputdirect-current source, specifically a battery 14, and the load capacitor12. A magnetic core member 16, having an input or power winding 18, ahold winding 20, and an output winding Z2 disposed in inductiverelationship therewith, is utilized to store energy from the inputsource 14 land effect a transfer of this energy to the load capacitor12. The hold winding 2t) also serves as a voltage sensing winding whenenergy is being transferred to the load capacitor 12. In practice, themagnetic core member 16 has a hysteresis loop such as to effect aminimum of energy loss during an energy transfer cycle of the inverterlll. A high Q powdered magnetic iron core member is `an example of acore member that has such a characteristic.

ln order to control the flow of current from the input source 14 throughthe input winding 18, to thus store energy in the magnetic core member16, an amplifying device, specifically, a p-n-p junction type transistor24 having control and load electrode means, specifically, an emitterelectrode 26, a collector electrode 28 and a base electrode 30, isinterconnected with the input winding 18 and with the input source 14.The latter interconnecting means includes a switch 32, having a movablecontact member 34 disposed to be actuated into engagement with astationary contact member 36, so that the energizing circuit to theinput winding can either be manually completed or interrupted. Asillustrated, a capacitor 33 may be connected in shunt circuitrelationship with the series circuit including the direct-current source14 and the switch 32 in order to render the current drain from the inputsource 14 substantially constant, thereby maximizing the efiiciency inenergy transfer from the direct-current source 14 to the load capacitor12.

In practice, the amplifying device 24 should have characteristics suchthat a maximum output current for the device is reached when a givencontrol signal is applied to the device and a decrease in output currentfrom the maximum to substantially zero value is efected when the controlsignal in the device is decreased sufiiciently.

For the purpose of eiecting a iiow of control current from the holdwinding 2G through the transistor 24, during the yback portion of theoperation, a parallel circuit 4i?, one branch of which includes acapacitor 42 and the other branch of which includes a non-linear device,such as a low voltage Zener diode 44, is interconnected between thelower side of the hold winding 2i), as shown, and the base electrode 30,of the transistor 24, the upper side of the hold winding 2li beingconnected to the emitter electrode 2d. The function of the capacitor 42and the Zener diode 44 will be described hereinafter.

In accordance with this invention, in order to regulate the magnitude ofthe voltage across the load capacitor i2, a series circuit including aZener diode 46 and a capacitor 4S is interconnected between the baseelectrode 30, of the transistor 24, and the emitter electrode 2e. Inoperation, the capacitor 4S functions to effect a brea"'- dofwn of theZener diode 46 after it has been charged up to a suiiicient value afterone or more flyback operations, to thereby apply a cut-oir voltage tothe transistor 24, to thus render it non-conductive, as will beexplained more fully hereinatfer. In order to provide a discharge pathfor the capacitor 4S once the Zener diode 45 has been bro-ken down inthe reverse direction and the transistor 24 is at the cut-oir" value, animpendance member, specifically an adjustable resistor Si), is connectedin parallel circuit relationship `with the capacitor 4S. In practice,the resistor Si) can be adjusted so as to change the time required forthe capacitor 48 to discharge from one voltage to another.

In operation, the Zener diode 44 functions to prevent a discharge of thecapacitor 4S through the hold winding once the Zener diode 46 braeksdown in the reverse direction and provides a path for current flow fromthe hold winding 20 through the emitter and base electrodes '25 and 30,respectively, of transistor 24 when the voltage across the capacitor 42is of suflicient value to break the Zener diode 44 down in the reversedirection. On the other hand, the capacitor 42 is connected in shuntwith the Zener diode 44 in order to provide a complete circuit from thehold winding Ztl through the emitter and base electrodes 26 and 30,respectively, of the transistor 24 so that when Zener diode 46 is notconducting in the reverse direction any change in voltage across thehold winding 26 of such polarity that the upper end of the hold winding20, as shown, is at a positive polarity with respect to its lower end,effects a current how through the emitter and base electrodes 26 and 3d,respectively, in such a direction as to increase the ow of current fromthe positive terminal of the source i4 through the input winding 18 tothus further increase the magnitude of the voltage across the holdwinding 2tlg to thereby effect a regenerative action in starting eachconducting cycle of the transistor 24.

A unilateral conducting member, specifically a rectitier S2, isinterconnected between the lower side of the hold winding 20, as shown,and the junction of the Zener diode 46 and the capacitor 48 in order tocause the voltage across the capacitor 48 to more closely approach thevoltage across the hold winding 20 during a yback pulse. In other words,there is a lower forward voltage drop across the rectifier S2 than thereis across the Zener diodes 44 and 46 combined. Further, since theforward characteristics of the two Zener diodes 44 and 4o may betemperature sensitive if not properly chosen, some inaccuracy can `beintroduced into the regulated terminal voltage appearing across the loadcapacitor l2 due to ambient temperature changes if the rectifier 52 isnot provided.

In order to render the load capacitor l2 responsive to the change influx in the magnetic core member 16 when the current ow through theinput winding 18 is decreasing and for a period of time thereafter whenthe transistor 24 is non-conductive, a unilateral conducting member,specifically a rectiiier 54, is connected in series circuit relationshipwith the load winding 22 and is so poled to prevent the iiow of currentthrough the load capacitor l2 when the transistor 24 is conducting andcurrent iiow through the input winding 13 is increasing. As shown, thehold winding 2i? and the load winding 22 are so wound on the magneticcore member 16 that when the current i'low through the input winding 1Sis increasing the upper end of the hold winding Ztl, as shown, is at apositive polarity with respect to its lower end and the lower end of theload winding 22, as shown, is simultaneously at a positive polarity withrespect to its upper end.

When the iiyback power inverter lil` is utilized as an electronicphoto-flash circuit, a suitable photo-flash bulb 56, having built-intriggering circuitry, is connected across the load capacitor l2. Inoperation, the bulb 56 is switched or triggered to eiect a discharge ofthe energy from the capacitor 12 through the photo-flash bulb 56.

The operation of the regulated flyback power inverter lltl will now bedescribed. Upon actuation ofthe movable contact member 34, of the switch32, to the circuit closed position with respect to the stationarycontact member 36, and upon any disturbance in the voltage across thehold winding 29 of such polarity that the upper end of the hold winding20, as shown, is at a positive polarity with respect to its lower end, acurrent lows through the emitter and base electrodes 26 and Sil',respectively, and the capacitor 42 in such a direction as to increasethe flow of current from the positive terminal of the source i4 throughthe input winding I8, to thus further increase the magnitude of thevoltage across the hold winding 20, to thereby etect a regenerativeaction in starting the irst conduction cycle of the transistor 24. Whenthe current flowing through the capacitor 42 charges the capacitor 42 tothe Zener level of diode 44 the Zener diode 44 breaks down in thereverse direction and control current continues to flow from the upperend of the holding winding 2U, as shown, through the emitter electrode26, the base electrode 3G, and the Zener diode 44 in the reversedirection, to the lower end of the hold winding 20. The current owthrough the input winding i8 increases substantially linearly,increasing the flux in the magnetic core member lo in the positivedirection, until a maximum collector current for the transistor 24 isreached for the given control current iiowing through the transistor 24from the hold winding 20. At this time, there is no further increase inthe magnitude of the current owing through the input winding .13 andthus the voltage across the hold winding 2i) decreases, therebydecreasing the magnitude of the collector or power current iiowingthrough the transistor 24 and the power winding 18. This decreasingcurrent through the input winding i8 effects a reversal of the polarityof the voltage across the hold winding 2@ so that the lower end of thehold winding 2i), as shown, is at a positive polarity with respect toits upper end. This latter induced voltage across the hold winding 20eiects a ilow of current from the lower end of the hold winding 2G, asshown, ythrough the rectiiier 52 in the forward direction, and thecapacitor 43 to the upper end of the hold winding 26, to thus charge thecapacitor 4E, during the time that the flux in the magnetic core memberlo is decreasing from its positive value, to essentially the magnitudeof the voltage across the hold winding 2u, which magnitude is in turnproportional by a turns ratio to the magnitude of the voltage across theload winding 22 which voltage is essentially equal to the voltage acrossthe load capacitor l2. Simultaneously, the stored energy in the magneticcore member 16 eiects a current tlow from the upper end of the loadwinding 22, as shown, through the rectifier 54 in the forward directionand the load capacitor l2, to the lower end of the load winding asses??22, to thereby increase the charge on the capacitor 12.

When the stored energy in the magnetic core member 16 has beencompletely transferred to the load capacitor 12, the voltage across allof the windings 18, 20 and 22 decreases to zero value and the abovedescribed operation is again repeated, to thereby charge the capacitor4S a further amount. After a number of flyback operations in whichflyback current iiows from the hold winding 20 through the capacitor 48,the capacitor 48 reaches a predetermined value which, at the terminationof the last iiyback operation, is sutlicient to effect a breakdown ofthe Zener diode 46 in the reverse direction, to thereby apply a portionof the voltage appearing across the capacitor 48 between the emitterelectrode 26 and the base electrode 30, of the transistor 24, to thusbias the transistor 24 sufficiently into cutoff as to prevent the abovedescribed regenerative action. Itis at this time that the voltage acrossthe load capacitor 12 reaches the regulated value.

Once the Zener diode 46 breaks down, and the transistor 24 is cut off,the capacitor 43 discharges through the resistor Sti and the transistor24 remains cut off for a predetermined time. After this predeterminedtime which is dependent upon the value to which the adjustable resistor50 has been set, the voltage across the capacitor 48 becomes insuiicientto effect a breakdown of the Zener diode 46 in the' reverse direction`and the inverter 10 is now conditioned to effect one or more energytransfer cycles. In the meantime the load capacitor 12 has leaked ol soas to effect a decrease of the voltage across it to a value below theregulated value `and the inverter goes through one or more energytransfer cycles to again charge up the capacitor 48 to such a value asto again break the Zener diode 46 down in the reverse direction and atthe same time return the voltage across the load capacitor 12 to theregulated value. Thus, the Zener diode 46 and the capacitor 48 and itsassociated adjustable resistor 50 function to maintain the voltageacross the load capacitor 12 at substantially the regulated value. Inpractice, the adjustable resistor 50 and the remainder of the circuitrymust be such that it requires at least one iyback operation to returnthe voltage across the load capacitor 12 to the regulated value.

The capacitor 48, upon discharge of the load capacitor 12 into thephoto-flash bulb 56, is not discharged to zero value through theadjustable resistor 5t) before the inverter 10 again goes through itscycle of operation, and several flyback operations occur before thevoltage across the hold winding 2@ is of suflicient value to efect afurther charging of the capacitor 4S. However, when the voltage acrossthe hold winding Ztl and the rectifier 52 becomes greater than thevoltage across the capacitor 48, the capacitor 48 is again charged upfurther and further in the manner hereinbefore described to thus againeffect a breakdown of the Zener diode 46 in the reverse direction andthus cut the transistor 24 off.

Referring to FIG. 2 there is illustrated another embodiment of theteachings of this invention in which like components of FIGS. 1 and 2have been given the same reference characters. The main distinctionbetween the apparatus and circuits of FIGS. 1 and 2 is that in theapparatus and circuits of FIG. 2 the input source 14 has been relocatedso as to be interconnected between the lower portion of the inputWinding 13 and the emitter electrode 26, of the transistor 24. Inaddition, the adjustable resistor 50 has also been relocated so as to beinterconnected between the negative terminal of the input source 14 andthe base electrode Sn, of the transistor 24. With the input source 14and the adjustable resistor Sil so relocated, the regulated iiybackpower inverter 64 shown in FIG. 2 starts more readily than does theflyback power inverter 1@ of FIG. 1. Specifically, with the adjustableresistor Sil so interconnected with the remainder of the apparatus andcircuits of FIG. 2 the input source 14 effects a bias of the transistor24 to an operating point wherein a given change in voltage between theemitter electrode 26 and the base electrode 3) initially effects alarger change in the collector current of the transistor 24 as comparedto the apparatus `and circuits of FIG. l and thus improves the startingcharacteristics of the inverter 64.

During that portion of the operation when the capacitor 48 effects abreakdown of the Zener diode 46 in the reverse direction so as to permita discharge of the capacitor 48 through the adjustable resistor e'l,this discharge current ows in this instance from the capacitor throughthe Zener diode 46 in the reverse direction, and the adjustable resistor50, to the negative terminal, of the input source 14.

it is to be noted that the rectifier 52 has been omitted from theinverter 64 of FIG. 2. When so omitted the Zener diodes 44 and 46provide a conducting path for charging the capacitor 48 and in someinstances the Zener diodes 44 and 46 may be so chosen that with a changein ambient temperature the characteristics of the Zener diodes 44 and 46so change that the regulated terminal voltage across the load capacitor12 is less affected. That is, an increase in ambient temperature causes`a decrease in forward voltage drop in Zener diodes 44 and 46 which willcause the capacitor 48 to charge to a slightly higher voltage at theincreased temperature and this will tend to compensate the highervoltage magnitude required to make Zener diode 46 break down in thereverse direction at the increased temperature.

Since the remaining operation of the regulated flyback power inverter 64is substantially the same as the operation of the regulated tiybackpower inverter 1t? of FIG. l, a further description of such operation isdeemed unnecessary.

The apparatus and circuits embodying the teachings of this inventionhave several advantages. For instance, the tlyhack power inverter ofthis invention has a high energy transfer etiiciency in charging acapacitive load from a low initial voltage to some higher voltage andthus when the inverter is utilized as an electronic photo-flash circuit,the recycle time for the photo-flash circuit is reduced. In addition, asimple and unique regulating means is provided for the inverter whicheffects non-asymptotic voltage regulation so as :to further reduce therecycle time when the inverter is utilized for instance, `as anelectronic photoliash circuit. The regulating means of this inventionfunctions in such a manner that when an indicator bulb (not shown) isconnected across an appropriate winding on the magnetic core member 16the brilliance of the indicator bulb (not shown) will diminish abruptlyto a readily distinguishable lower level of brilliance when theregulated terminal voltage across the capacitor 12 is reached. This in aphotoliash application becomes an laccurate indicator of the time whenthe load capacitor 12 is fully charged to the regulated value. Further,the power transistor of the inverters of this invention operate at arelatively low frequency when regulating at the terminal voltage, thusminimizing the energy loss in the transistor in going from the on to offcondition. Also, the output or power rectiier of the inverters of thisinvention as applied to an electronic photo-Hash circuit can have alower voltage rating than the power rectier of other conventionalinverter circuits that are utilized for electronic photo-dash purposes.

Since certain changes may be made in the above described apparatus andcircuits, and different embodiments of the invention may be made withoutdeparting from the spirit and scope thereof, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

I claim as my invention:

l. In a yback inverter adapted to be connected to a source ofdirect-current to effect an output voltage, the combination comprising,a magnetic core member, input winding means disposed in inductiverelationship with said magnetic core member, an amplifying device havingcontrol and load circuit electrode means and having characteristics suchthat a maximum output current for said device is reached when a givencontrol `signal is applied to said device and a decrease in outputcurrent from said maximum to substantially zero value is effected whensaid control signal is decreased suciently, circuit means for soconnecting said control and load circuit electrode means and said inputWinding means in circuit relationship with one another and with saidsource, that said amplifying device `controls the flow of current `fromsaid source through said input winding means, a series circuit includinga voltage reference device and a capacitor, lthe series circuit beingdirectly connected to said control and load circuit elect-rode means soas to maintain said amplifying device in a substantially non-conductivestate when said capacitor has a given voltage thereacross suiiicient tomake said voltage reference device conductive, discharge means foreffecting a reduction in the magnitude of said given voltage appearingacross said capacitor, hold winding means disposed in inductiverelationship With said magnetic core member, other circuit means forinterconnecting said control and load circuit electrode means with saidhold Winding means so as to effect a ow of control current from saidhold Winding means through said amplifying device when the ow of currentfrom said source through said input winding means is increasing to thusincrease the iiux in said magnetic core member in the positive directionand effect a flow of current lfrom said hold Winding means through saidcapacitor when the flux in said magnetic core member is decreasing fromsaid positive value, to thus charge said capacitor, after one or moreiiybacks, to said given value of voltage suthcient to make said voltagereference device conductive, to thereby cut said amplifying device oif,and output Winding means disposed in inductive relationship with saidmagnetic core member, said output voltage in operation appearing at saidoutput Winding means.

2. In a iiyback inverter adapted to be connected to a source ofdirect-current to effect an routput voltage, the combination comprising,a magnetic co-re member, input winding means disposed in inductiverelationship with said magnetic core member, an amplifying device havingcontrol and load electrode means and having characteristics such that amaximum output current for said amplifying device is reached When agiven control signal is applied yto said amplifying `device and adecrease in output current from said maximum to substantially zero valueis eected when said control signal is decreased sufiiciently, circuitmeans for so connecting said control and load electrode means and saidinput winding means in circuit relationship with one another and Withsaid source that said amplifying device controls the flow of currentfrom said source through said input Winding means, a series circuitincluding a voltage reference device and a capacitor, the series circuitbeing directly connected to said control and load electrode means so asto maintain said amplifying device in a substantially nonconductivestate When said capacitor has a given voltage thereacross suicient tomake said voltage reference device conductive, discharge means foreffecting a reduction in the magnitude of said given voltage appearingacross said capacitor, hold Winding means `disposed in inductiverelationship with said magnetic core member, other circuit means forinterconnecting said control and load circuit electrode means With saidhold Winding means so as to effect a flow of control current from saidhold winding means through said amplifying device when the flow ofcurrent from said source through said input Winding means in increasingto thus increase the flux in said magnetic core member in the positivedirection and eiiect `a flow of current from said hold Winding meansthrough said capacitor when the iiux in said magnetic core member isdecreasing from said positive value, to thus charge said capacitor,after one or more iiybacks,

to said given value of voltage sufncient to make said voltage referencedevice conductive, to thereby cut said amplifying device oi, said othercircuit means including a non-linear `device to substantially limit thedischarge of said capacitor through said hold winding means once saidvoltage reference device becomes conductive, and output Winding meansdisposed in inductive relationship With said magnetic core member, saidoutput voltage in 0peration appearing at said output Winding means.

3. In a flyback inverter adapted to be connected to a source ofdirect-current to effect an output voltage, the combination comprising,a magnetic core member, input Winding means disposed in inductiverelationship with said magnetic core member, an amplifying device havingcontrol and load electrode means and having characteristics such that amaximum output current for said amplifying device is reached When agiven control signal is applied to said amplifying device and a decreasein output current from said maximum to substantially Zero value iseifected when said control signal is decreased suliciently, circuitmeans for so connecting said control and load electrode means and saidinput Winding means in circuit relationship with one another and Withsaid source that said amplifying device controls the flow of currentfrom said source through saidinput Winding means, a series circuitincluding a voltage reference device and a iirst capacitor, the seriescircuit being directly connected to said control and load electrodemeans so as to maintain said amplifying device in a substantiallynon-conductive state when said iirst capacitor has a given voltageacross and is sufficient to make said voltage reference deviceconductive, discharge means for eifecting a reduction in the magnitudeof said given voltage appearing across said rst capacitor, hold Windingmeans disposed in inductive relationship with said magnetic core member,other circuit means for interconnecting said control and load electrodemeans with said hold Winding means so as to effect a iiow of controlcurrent from said hold winding means through said amplifying device whenthe flow of current from said source through said input Winding means isincreasing, to thus increase the ux in said magnetic core member in thepositive ldirection and effect a flow of current from said hold Windingmeans through said rst capacitor when the flux in said magnetic coremember is decreasing from said positive value, to thus charge said firstcapacitor, after one or more flybacks, to said given value of voltagesuiiicient to make said voltage reference device conductive, to therebycut said amplifying device off, said other circuit means including aparallel circuit, one branch of which includes a Zener diode and theother branch of which includes a second capacitor, said parallel circuitin operation functioning to substantially limit the discharge of saidlirst capacitor through said hold Winding means once said voltagereference device becomes conductive and permit the ow of control currentfrom said hold Winding means through said amplifying device when theflow of current from said source through said input winding means isincreasing, and output Winding means disposed in inductive relationshipWith said magnetic core member, said output voltage in operationappearing at said output Winding means.

4. In a iiyback inverter adapted to be connected to a source ofdirect-current to effect an output voltage, thecombination comprising, amagnetic core member, input Winding means disposed in inductiverelationship with said magnetic core member, an amplifying device havingcontrol and load electrode means and having characteristics such that amaximum output current for said amplifying device is reached when agiven control signal is applied to said amplifying device and a decreasein output current from said maximum to substantially zero value iseffected when said control signal is decreased sufficiently, circuitmeans for so connecting said control and load electrode means and saidinput Winding means in series circuit relationship with one another andwith said source that said amplifying device controls the flow ofcurrent from said source through said input winding means, a seriescircuit including a voltage reference device and a capacitor, saidseries circuit being directly connected to said control and loadelectrode means so as to maintainvsaid amplifying device in asubstantially non-conductive state when said capacitor has a givenvoltage thereacross sufficient to make said voltage reference deviceconductive, discharge means for eiecting a reduction in the magnitude ofsaid given voltage appearing across said capacitor, hold winding meansdisposed in inductive relationship with said magnetic core member, othercircuit means for interconnecting said control and load electrode meanswith said hold winding means so as to effect a ow of control currentfrom said hold winding means through said amplifying device when theflow of current from said source through said input winding means isincreasing to thus increase the flux in said magnetic core member in thepositive direction and effect a ow of current from said hold windingmeans through said capacitor when the flux in said magnetic core memberis decreasing from said positive value, to thus charge said capacitor,after one or more ybacks, to said given value of voitage sucient to makesaid voltage reference device conductive, to thereby cut said amplifyingdevice off, means for eifecting bias current for said amplifying deviceto thus bias said amplifying device to an `operating point wherein agiven rate of change in the lux in sai' magnetic core member effects agreater change in the magnitude of the control current from said holdwinding means through said amplifying device to thereby improve thestarting characteristics of said amplifying evice, said other circuitmeans including a non-linear device for substantially limiting thedischarge of said capacitor through said hold winding means once saidvoltage reference device becomes conductive and preventing the shortcircuiting of said bias current through said hold winding means when theux in said magnetic core member is not changing, and output Windingmeans disposed in inductive relationship with said magnetic core member,said ouput voltage in operation appearing at said output winding means.

5. In a yback inverter adapted to be connected to a source ofdirect-current tot elfect an output voltage, the

said magnetic core member, a transistor having a control electrode andtwo load electrodes, circuit means for interconnecting said sourcebetween one side of said input winding means and one of said two loadelectrodes and for connecting the other of said two load electrodes `tothe other side of said input winding means so that said transistorcontrols the ow of current from said source through said input windingmeans, a bias resistor connected between said control electrode and thejuncture of said source and said input winding means for effecting abias current for said transistor, a series circuit including a voltagereference device and a first capacitor, the series circuit beingconnected between said control electrode and said one of said two loadelectrodes, hold winding means disposed in inductive relationship withsaid magnetic core member, a parallel circuit one branch of whichincludes a second capacitor and a non-linear device, other circuit meansfor interconnecting said parallel circuit between said control electrodeand one side of said hold Winding means and for connecting the otherside of said hold winding means to said one of said two load electrodesso as to effect a ilow of control current through said transistor whenthe ow of current from said source through said input winding means isincreasing, to thus increase the flux in said magnetic core member inthe positive direction and effect a low of current from said holdwinding means through said first capacitor when the flux in saidmagnetic core member is decreasing from said positive value, to thuscharge said lirst capacitor, after one or more ilybacks, to a valuesuicient to make said voltage reference device conductive, to therebycut said transistor o, said non-linear device functioning tosubstantially limit the discharge of said rst capacitor through saidhold winding means once said voltage reference device becomes conductiveand to prevent the shorting of said bias current through said holdwinding means when the iluX in said magnetic core member is notchanging, and output winding means disposed in inductive relationshipwith said magnetic core member, said output voltage in operationappearing at said output winding means.

References Cited in the le of this patent UNITED STATES PATENTS

